1. Field of the Invention
The present invention relates to an injection unit for holding of medicament, the injection unit comprising a hollow, cylindrical barrel terminating in a neck comprising an outwardly directed annular projection at its distal end, a flexible neck cap, a holding cap engaging the neck cap from the outside and comprising a proximal section in the form of a skirt having one or more interior projections at its proximal end for engagement behind the annular projection of the barrel neck, and a distal section having means for attaching a needle thereto, and a locking ring provided on the outside of the skirt at its proximal end for locking the holding cap in its engagement position.
2. Description of the Related Art
Injection units of the type mentioned above having a removable barrel neck seal allow lyophilization of the medicament contained in the barrel to be conducted in situ through the neck of the barrel.
European patent publication No. 0,191,122 discloses an injection unit in the form of a syringe and of the type mentioned in the introductory part. The syringe comprises a neck cap which extends from the proximal end of the neck of the barrel to the distal end of the holding cap and which has a passageway therethrough sealed with a cap mounted on the neck of the holding cap. The distal end of the covering cap has the form of a Luer-cone and, prior to use, the covering holding is removed and a needle is mounted on the holding cap.
In practical use, however, the above mentioned prior art syringe has been found to suffer from an essential drawback. In handling the syringe it is difficult to avoid that the holding cap is exposed to side-pressure, and as a result it frequently occurs that the holding cap slips out of its engagement position.
When the syringe is accidentally dismantled in this manner, the syringe and the medicament contained therein which may be quite expensive, must be discarded due to risk of contamination of the medicament.
Attempts have been made to overcome the above mentioned drawback by locking the holding cap in the engagement position by means of a locking ring which is mounted on the outside of the skirt of the holding cap at its proximal end following the engagement of the holding cap on the barrel neck. However, such a locking ring in combination with the prior art holding caps have proved to be insufficient as a measure of keeping the holding cap in place.